From the book's introduction:"
"Circe (pronounced sir-see) is a skill based gaming system designed for medieval fantasy game worlds where magic is powerful but rare. This system is intended to realistically model life as an adventurer in a medieval world in which monsters and magic really do exist, and gods do look down from the heavens.
"Circe is also the first Computer Aided Roleplaying Game. This game needs the use of a computer by players and referee to generate characters and adventures. The use of a computer is by no means required, however. Nearly all of the math is simple arithmetic. The reason so many equations are used is to make it simpler to model all of the rules in a computer program. Because it was designed with computers in mind, it’s being used in the WorldForge online gaming system."
This book is reffered to as both the "Core Ruleset" and just as "Circe."